The present invention relates to the development of planographic printing plates, and especially lithographic printing plates having an imaged photosensitive coating with regions that are soluble in an alkaline developer solution.
Historically, the processing of positive plates involves immersion of the plate in a sump of developer as it passes through a plate processor. The plate then exits the sump, and is typically subjected to a rotating brush or molleton and a nip roll set prior to being rinsed. This method of development relies entirely on the chemical dissolution of the solubilized coating to produce the plate. The developer is an alkaline solution typically containing an alkali metal silicate and/or alkali metal hydroxide along with other wetting agent/surfactants. The temperature of the developer is critical, and must be controlled over a small range. The development is influenced by any flow dynamics (e.g. even small eddy currents) in the sump. This presents difficulties to get uniform development or consistent development from plate to plate. It is also difficult to assure that shadows and background areas clean out without attacking highlight dots in halftones.